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Cable Editor OverviewThe cable editor includes the following eleven pages of properties.

The properties associated with cables of the electrical distribution system the one-line diagram can be enteredin this data editor.

ETAP allows you to place cables in the one-line diagram to connect two elements (two buses, a motor to a bus,or a static load to a bus) and place the same cable in a cable raceway. However, you can add cables to the

one-line diagram without placing them in a cable raceway, or add cables to the raceway without adding them tothe one-line diagram. To explain this further, here are the definitions of the four types of cables in ETAP.

Info Page

Impedance Page

Physical Page

Protection Page

Routing Page

Loading Page

Ampacit y Page

Sizing Page

Reliability Page

Remarks Page

Comment Page

1. One-Line Cableappears as a graphical element onthe one-line diagram. This is a cable that you add to theone-line diagram to connect buses, but has not beenpreviously routed through any cable raceway, i.e., doesnot exist in any raceway.

2. Equipment Cablecan be attached to equipment suchas motors and static loads, but do not appear graphicallyas a separate element on the one-line diagram. This is acable that you add to equipment from the equipmenteditor, and has not been placed in any raceway.

3. Raceway Cableis used exclusively within the cableraceway system only. This is a cable, which is routed

through a raceway such as an underground cablesystem, but does not exist in the one-line diagram or asan equipment cable.

4. Compound Cablerepresents a cable that is includedin the cable raceway system as well as the one-linediagram (either as a one-line or equipment cable). Thiscable is added to the one-line diagram as a one-line orequipment cable, and then is placed inside a raceway(graphically or from Cable or Raceway Editors). Or,conversely, the cable is added as a raceway cable, and

then is placed in the one-line diagram as a one-linecable.

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Compound Cables

The following paragraphs describe three different methods of changing a one-line or equipment cable to acompound cable (routing an existing cable through a raceway):

From the underground raceway presentation, click the Existing Cable button on the Edit toolbar and place thecable in the desired location. Then select the desired one-line or equipment cable from the selection boxprovided.

From the Cable Editor, Routing page, route the cable through any raceway that exists in the system. Thesecables are attached or associated with the raceways without being placed in a specific location inside theraceway. From the underground raceway system, you can then graphically move the cable to the desiredlocation.

To graphically place a one-line cable inside a cable raceway, select the cable from the one-line diagram and

press +Click (holding the mouse button down). The pointer will now have an X over it indicatingthat you can only drop it in an underground cable system. Hold the mouse button down until you have movedthe pointer from the one-line view to the UGS view, place the pointer on top of a conduit or the desired locationin a raceway, and then release the mouse button. Since an equipment cable is not displayed graphically in theone-line diagram, you can only use the first two methods explained above to route an equipment cable.

Note: a raceway cable cannot be changed to an equipment cable. However, an equipment cable can bechanged to a compound cable.

You can add a raceway cable to the one-line diagram and make it a compound cable in two ways:

1. First select the cable from the raceway and cut it to the Dumpster. Now you can add it back to the same

raceway as an existing cable while a copy of it stay in the Dumpster. To add this cable to the one-linediagram, use the Move From Dumpster command.

2. Select the cable from the raceway and then press +Click (holding the mouse button down). Thecursor will change to a cable shape with an X over it. Hold the mouse button down until you have moved thecursor from the UGS view to the desired location on the one-line view, and then release the mouse button.

Page 2 of 2Cable Editor Overview

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Info Page - Cable EditorYou can specify the cable ID, From and To bus ID, In/Out of Service, Length, Size, number of conductors perphase, and Library link from within the Info page of the cable editor.

Cable Type

This information is displayed on top of every page of the Cable Editor to reflect the cable type and size selectedfrom the Cable Library. This is a partial list of the library header which includes the library source name (ICEA,NEC), rated voltage (0.6, 5, 15 kV), voltage class (100%, 133%), # of conductors per cable (1/C, 3/C),conductor type (CU, AL), insulation type (Rubber, XLPE), installation type (Magnetic/Non-Mag.), and cable size(350 kcmil, 180 mm2). The unit for cable sizes will be in AWG/kcmil for English unit cables and mm2 for Metricunit cables. Note: ETAP provides list of all available cable sizes from the selected library for quick selection.

If you change the cable size, all library data will be substituted from the cable library into the Cable Editor. Ifyou modify any data that was extracted from the library, the color of Cable Type will change to a dark blue colorto indicate that there is a conflict between the editor and library data.

Info

ID

Entering a unique ID with up to 25 alphanumeric characters.

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ETAP automatically assigns a unique ID to each cable. The assigned IDs consist of the default cable ID plusan integer, starting with the number one and increasing as the number of cables increase. The default cable ID(Cable) can be changed from the Defaults Menu in the menu bar or from the Project View.

From & To

Bus IDs for the connecting buses of a cable branch are designated as From and To buses. If a terminal of abranch (From or To) is not connected to any bus, a blank entry will be shown for bus ID. To connect orreconnect a branch to a bus, select a bus from the list box. The one-line diagram will be updated to show thenew connection after you click OK. Note: you can only connect to buses that reside in the same view where thebranch resides, i.e., you cannot connect to a bus that resides in the Dumpster or in another composite network.

For 3 Phase Cables, only 3 Phase buses will be displayed in the drop down lists. For Single Phase Cables onlysingle phase buses will be displayed.

If a branch is connected to a bus through a number of protective devices, reconnection of the branch to a newbus from the editor will reconnect the last existing protective device to the new bus, as shown here whereBranch X is reconnected from Bus10 to Bus4.

ETAP displays the nominal kV of the buses next to the From and To bus IDs for your convenience.

Single Phase Cable can also be connected to Phase Adapters. If the Cable is connected as such, then thePhase Adapter ID will be shown in the Primary or Secondary field.

In/Out of Service

The operating condition of a cable can be selected by choosing either the In Service or Out of Service options.The properties of an Out of Service branch can be edited like an In Service branch. However, an Out of Servicebranch will not be included in any system studies. When Continuity Check is activated, an Out of Servicebranch automatically becomes dimmed in the one-line diagram. All the loads and branches energized solelythrough an Out of Service branch will also be de-energized and become dimmed.

Note: the In/Out of Service option is an engineering property, which is independent of the configuration status.Therefore, you can set a branch to be In Service for the Base Data and Out of Service in the Revision Data.

Connection

Cables can be defined as 3 Phase or 1 Phase cable by selecting any of the following selections:

3 PhaseDefines the cable as a three-phase cable. This cable can be connected only to three-phase buses.

1 Phase



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Defines the cable as a single-phase cable.

Library

Library Button

To select cables from the Cable Library, click the Library button and the Cable Library Quick Pick will appear.From the Library Quick Pick select the Cable Library type and size at the same time. Note: after the selectedCable Library type, size, and parameters are transferred to the Cable Editor, the cable size can be changeddirectly from the Cable Editor and the cable parameters are refreshed from the library. Therefore, the mostimportant action is to select the correct Cable L ibrary type from the Cable L ibrary Quick Pick. When data aretransferred from the Cable Library, ETAP automatically corrects the cable reactances for the system frequency.

Link to Library

A library link is also available to use Cable Library data instead of the stored cable impedance and dimensionparameters that are displayed in the Cable Editor. Note: Link to Library is only used at the time of execution ofstudies. For example, when you run a load flow study, ETAP uses the cable library type and size as anidentifier to extract data from the Cable Library. This option is provided so that you can globally update thecable parameters by changing the library data only.

Equipment

FDR Tag

Enter the feeder tag in this field, using up to 25 alphanumeric characters.

Name

Enter equipment name, using up to 50 alphanumeric characters.

Description

Enter equipment description, using up to 100 alphanumeric characters.

Length

Length

Enter the length of the cable and select the unit from the list box. The units of length available are: feet, miles,meters, and kilometers.Note: every cable in the system can have a different unit.

Tolerance

Enter the percent of tolerance in line length. The Adjustments page in the analysis modules can be used toconsider +/- % tolerance in line length, effectively increasing or decreasing the impedance based on the type ofstudy being performed.



# Conductors / Phase

Enter the number of conductors per phase, i.e. if 2-3/C cables or 6-1/C cables are used (6 conductors total),then the number of conductors per phase is equal to two (2).

Cable Overview

Impedance Page

Physical Page

Protection Page

Routing Page

Loading Page

Ampacit y Page

Sizing Page

Reliability PageRemarks Page

Comment Page



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Impedance Page - Cable Editor

Impedance

Positive and Zero Sequence Resistances (R & R0)

Enter positive and zero sequence resistances at the base temperature, in ohms or ohms per unit length, perconductor. This is for each conductor, not the total resistance per phase. ETAP corrects these resistances fordifferent studies based on the specified temperature limits. The zero sequence resistance is used only forunbalanced fault current calculations.

Positive and Zero Sequence Reactances (X & X0

)

Enter the positive and zero sequence reactance levels, in ohms or ohms per unit length, per conductor. This isfor each conductor, not the total reactance per phase. These reactance levels must be entered at the systemoperating frequency specified for this data file. When data is recalled from English (60 Hz) or Metric (50 Hz)libraries, ETAP automatically corrects for the system operating frequency. After this value is entered here,

ETAP will not make any adjustment to this value. The zero sequence reactance is used only for unbalancedfault current calculations.

Positive and Zero Sequence Susceptances (Y & Y0)

Page 1 of 3- Impedance Page


Enter positive and zero sequence susceptance levels in siemens or siemens per unit length, for each

conductor. If the value of Y>0, the circuit element is treated as a pi equivalent, with one-half of the chargingsusceptance connected to neutral at each end of the circuit. If Y=0, the cable is treated as a simple impedance.This susceptance must be entered at the system operating frequency specified for this data file.

When data is recalled from English (60 Hz) or Metric (50 Hz) libraries, ETAP automatically corrects for thesystem operating frequency. After this value is entered here, ETAP will not make any adjustment to this value.The zero sequence susceptance is used only for unbalanced fault current calculations.

Units

Select impedance units as ohms per unit length or ohms. With the selection of ohms per unit length, a lengthshould also be designated, including a unit from the list box. Units available are: feet, miles, meters, andkilometers.

Cable Temperature

Base Temperature

Enter the conductor base temperature (in degrees Celsius) at which the cable resistances are entered.

Minimum & Maximum Temperature

Two conductor temperature limits (in degrees Celsius) may be entered for adjusting positive and zerosequence resistances (R and R

0) for different studies. The first limit is the minimum operating temperature; the

second limit is the maximum operating temperature. ETAP will use the most conservative temperature limit foreach study type. For example:

If this correction is not wanted, set both minimum and maximum temperature limits equal to the basetemperature. ETAP uses the following equations for temperature corrections:

R = R ( 234.5 + Tc )/( 234.5 + Tb ) Copper Conductors

R = R ( 228.1 + Tc )/( 228.1 + Tb ) Aluminum Conductors

where:

R = Resistance at base temperature Tb

R= Resistance at operating temperature Tc

Tb = Conductor base temperature inC

Tc = Conductor temperature limit inC

If the conductor type is not known (no cable library is selected), ETAP defaults to copper as a conductor type.

Cable Overview

Info Page

Physical Page

Temperature Limit

Min Max

Load Flow X

Short-Circuit X

Motor Starting X

Transient Stability X



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Protection Page

Routing Page

Loading Page

Ampacit y Page

Sizing Page

Reliability Page

Remarks Page

Comment Page



Physical Page - Cable Editor

Dimensions

The physical properties of cables entered in this page are only used for calculating engineering data neededfor cable ampacity derating studies (U/G Raceway Systems) only.

Rdc

This is the DC resistance of the cable in micro ohm at 25 degrees C.

Cable OD

This is the overall cable outside diameter including the sheath, armor and/or jacket in inches or centimeters.

Conductor OD

This is the physical outside diameter of the conductor in inches or centimeters.

Insulator tThis is the thickness of the conductor insulation in mil or mm.

Sheath t

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This is the thickness of cable sheath or armor in mil or mm. This value becomes zero if the Sheath/Armoroption is set to None.

Jacket t

This is the thickness of outer cable jacket in mil or mm.

Weight

This is the weight of the cable in lbs/1000ft or kg/km.

Max. Tension

This is the maximum tension that the cable can withstand without damage in lbs/kcmil or kg/mm2.

Max. SW

This is the maximum Side Wall pressure in lbs/ft or kg/m.

Conductor Construction

Conductor construction is used for determining ks and kp parameters, which are used for calculating the ac todc ratio parameters. Several available choices of conductor construction are:

ConRnd Concentric Round None Coated None Treated

ConRnd-Coated Concentric Round Coated None Treated

ConRnd-Treated Concentric Round None Coated Treated

CmpRnd-Treated Compact Round None Coated Treated

CmpSgm Compact Segmental None Coated None Treated

CmpSgm-Coated Compact Segmental Coated None Treated

CmpSgm-Treated Compact Segmental None Coated Treated

CmpSct-Treated Compact Sector None Coated Treated

The coating is tin or alloy. The term Treated implies a completed conductor, which has been subjected to adrying and impregnating process similar to that employed on paper power cables.

Shielding

Choose shielded or not shielded.

Sheath/Shield End Connection

Choose either the open or grounded option. Grounded option implies that the sheath and shield are groundedat more than one location.

Sheath/Armor Type

Jacket TypeJacket Types available:

None

Lead Sheath

Aluminum Sheath

St Armor/30 dg/ 15 W















None NeoPrene RHH THW



Cable Overview

Info Page

Impedance Page

Protection Page

Routing Page

Loading Page

Ampacit y Page

Sizing Page

Reliability Page

Remarks Page

Comment Page

Paper

PEXLPE

EPR

SBR

Rubber

Rubber1

Rubber2

PVC

FEPFEPB

MI

MTW

PFA

PFAH

RH

RHW

SASIS

TA

TBS

TFE

THHN

THHW

THWN

TWUF

USE

V

XHHW



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Protection Page - Cable Editor

The Protection page provides options related to cable protection. It includes options for plotting the cable thermal capability (I 2t)curve on a Star View, updating short-circuit current, and cable protection information specifically for cable installations compilingwith BS 7671 standard. Cables do not have unlimited power handling capability and need protection to prevent operationbeyond that capability in the event of short-circuit conditions. The main cause of reduced cable lifetime is high temperaturegenerated by continuous overloading or uncoordinated fault protection. Cable protection is required to protect personnel andequipment.

Thermal Capability

Plot I2

t

When this option is selected, a cable thermal capability curve will be plotted on the active Star View.

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This option is active only when a cable is selected from the library.

For a new cable, Plot I2t option is unavailable, as shown below.



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The thermal capability curve is an I2t characteristic curve that depends on the following pa rameters:

Conductor temperature

Insulation type

Number of conductors per phase

The ambient temperature of air is assumed to be 40C and the fusing temperature of copper is 1083

C. The thermal capability

curve is always drawn between 1 to 10 seconds.

Conductor Temperature

When a cable is selected from the library, the thermal capability curve can be plotted based on operating conductor temperatureor base (manufacturer) conductor temperature. This temperature is the initial temperature of the cable before a fault or overloadcondition.

The base conductor temperature (Tc) is available from the library and is displayed on the Ampacity page of the Cable Editor.

If the cable is applied where the conductor temperature does not match the manufacturer specified base temperature, then theoperating temperature value can be modified to display the appropriate thermal capability curve. If the operating conductor

temperature is lower than the base conductor temperature, then the cable will have higher thermal capability.

Reference kV

Calculated Base kV

This kV value is automatically updated with terminal bus base kV when you Run/Update Short-Circuit kA from the Star-Protection Device Coordination mode and at l east one cable terminal bus is faulted. This is a display only field.

Short-Circuit Current (Sym. rms)

This group allows you to specify the maximum and minimum short-circuit current when the terminal bus of the cable is faulted.These short-circuit current are used for cable sizing as well as for determining the equivalent system impedance. The short-



circuit current can also be updated automatically when you Run/Update Short-Circuit kA from the Star-Protection DeviceCoordination mode.

Calculated

Select Calculated to let ETAP update Max. Fault kA, Min. Fault kA and X/R. These values are updated by running Run / UpdateShort Circuit kA in Star mode. Max. kA is updated with Cycle kA for standard ANSI and Max Short-Circuit Current forstandard IEC. Min. Fault kA and X/R is updated with 30 Cycle kA for standard ANSI and M in. Short-Circuit Current for IEC. Ifboth terminal buses of the cable are faulted the fault kA from the bus that has bigger Max/ Fault kA will be used.

When this option is selected the kA and X/R fields in this group become display only.

User-Defined

You may enter the Max. kA, Min. kA and X/R by selecting the User-Defined option. Once this option is selected, the kA and X/Rfields in this group become editable.

Maximum kA

Enter the maximum short-circuit current in kA when cab le terminal bus is faulted. Based on this current, the positive sequenceimpedance of the equivalent system is calculated. It is assumed that the negative sequence impedance of the equivalent systemis the same as that of positive sequence.

Minimum kA

Enter the maximum short-circuit current in kA when cab le terminal bus is faulted. For a three-phase system, this generally is theshort-circuit current for a line-to-ground fault. Base this current, ETAP calculates the zero sequence impedance of the equivalentsystem.

X/R

This is the X/R for the faulted terminal bus of the cable.

Pin (Disable Update)

This check box is enabled only when the Calculated option is selected. When this option is selected, the Fault kA fields will notbe updated when you Run / Update Short Circuit kA in Star mode.

Protective Device

Overload Protection

This section is used only for BS 7671 based cable sizing. You may select the User-Defined or None option for overloadprotection. When the User-Defined option is selected, the In, I2 and BS 3036 fields will be enabled.

In Nominal current of overload protection device in amperes.

I2 Operating current of overload protection device in amperes.

BS 3630

Check BS 3036 if the overload protection is a Fuse to BS 30 36. This field is applicable only when the BS 7671 is selected as theinstallation standard in the Ampacity page.

Short-Circuit Protection

Select User-Defined or None for short-circuit protection. If User-Defined is selected, user can enter the Short-Circuit ProtectionTime which is used for cable sizing.

Time

Enter the time of maximum three-phase short-circuit time in seconds. This time is used in cable sizing if Short-Circuitrequirement is checked on the Sizing page.

Protective Grounding Z

This section is not used in this release. It is only applicable to BS 7671 based cable sizing. Enter the R and X values in Ohm forProtective Grounding. This is the total value of circuit protective conductor (CPC) impedance and customer earthing conductorimpedance.

Cable Overview

Info Page

Impedance Page



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Physical Page

Routing Page

Loading PageAmp acit y Page

Sizing Page

Reliability Page

Remarks Page

Comment Page



Routing Page Cable EditorThe Routing page provides lists of routed raceways and available raceways. The cable ID and raceway typeare shown for both the routed and available raceways.

Routed Raceways

This is a list of raceways through which this cable is routed. When you add a raceway to this list (by using theinsert or add buttons), the cable is placed in a container attached to the raceway without being placed in anyspecific conduit or location.

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When you bring up the graphical editor for the underground systems, you will see the cables in a container ofcables that are assigned to this raceway but not assigned to a specific conduit. This container is attached to theraceway and will disappear when it is empty. You must select and graphically move the cable from theunassigned cable container to the desired location.

This is a list of all existing available raceways in this project, i.e., raceways that this cable can be routedthrough. Note: since you cannot route a cable twice through a raceway, this list does not include the racewayslisted under Routed Raceways.

Available Raceways

This is a list of all existing available raceways in this project, i.e., raceways that this cable can be routedthrough. Note that since you cannot route a cable twice through a raceway, this list does not include theraceways listed under Routed Raceways.

Cable Overview

Info Page

Impedance Page

Physical Page

Protection PageLoading Page

Ampacit y Page

Sizing Page

Reliability Page

Remarks Page

Comment Page

Insert: Route this cable through the selected raceway from the availableraceway list ,i.e., insert the selected raceway to the list of routed raceways.

Add: Route this cable through the selected raceway from the availableraceway list ,i.e., add the selected raceway to the list of routed raceways.

Cut: Unroute this cable from the selected raceway.

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Loading Page - Cable EditorThe Loading Page provides information regarding cable loading (amp) and other parameters, which are used incable ampacity derating (Underground Raceway System) and cable sizing calculations.

Operating Load / Current

The operating load is specified in amps. This value is used for steady-state temperature calculation or as theinitial value of the cable load profile for the transient temperature calculation. The operating Avg. Phase A,Phase B, and Phase C can be updated with the results from load flow studies. You can do this by checking theUpdate Cable Load Amp option in the Info Page of the Load Flow and Unbalanced Load Flow Study Cases.

Growth Factor (GF)

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The Projection Multiplying Factor (MF) must be specified in percent. This value is used to indicate future loadprojection (load reduction or growth). You can select the option to use this Projection Multiplying Factor forcable temperature calculations from the Cable Ampacity Derating Study Case.

Loading Current for Sizing

Operating Current

The operating load current specified for this cable in the Loading page will be used if this option is selected.

Full Load Amps o f Element

The continuous current rating (rated current or FLA) of the selected element will be used for sizingrequirements. The motor ID is displayed here for motor equipment cables and the FLA of the motor is used.

User-Defined

Use this option to enter any value for the cable current.

NEC 430.6

The ampacity of the equipment cables is based on the motor ratings as determined by section 430.6 of NECcode. The current, in Amps, is derived based on the following:

UnderGround Raceway (UGS)

Load Factor

The load factor is the ratio of average load to peak load in percent. Use the following equation to calculate theload factor:

Load Factor = 100 ( kWi x Ti )/( kWp x Tt ) % = 100 E/( kWi x Tt ) %

where

i = Interval of time when the load is non-zero

kWi = Load at interval i

Ti = Number of hours of interval i

Mot or Ty pe Moto r Namepl at eHP

(or equivalent inkW)

Motor RatedkV

MotorConnection

NECTable

Number

DC Motor 1/4 to 200 0.090 to 0.550 430.247AC Induction 1/6 to 10 0.115 to 0.23 Phase-to-

Ground430.248

ACSynchronous

1/6 to 10 0.115 to 0.23 Phase-to-Ground

430.248

AC Induction 1/2 to 200 0.115 to 2.3 Phase-to-Phase 430.249

ACSynchronous

1/2 to 200 0.115 to 2.3 Phase-to-Phase 430.249

AC Induction 1/2 to 500 0.115 to 2.3 3-Phase 430.250

ACSynchronous

25 to 200 0.23 to 2.3 3-Phase 430.250



kWp = Peak load

Tt = Ton + ToffTon = Total hours when the load is on

Toff = Total hours when the load is off

E = Energy (kWh) consumed by load over the interval

If the cable carries load (current) at every interval, then the equation can be simplified to the percentage of timethat the cable will be carrying the current:

Load Factor = 100 Ton/Tt %

= 100 % (if it carries the load for 24 hours per day)

IEC 287 method ignores the load factor. It uses 100% Load factor for the calculation of the conductortemperature.

Sheath/Armor Current

The sheath/armor current can be specified as a percent of cable load current. This value indicates the amountof neutral or ground current that is carried by sheath or armor, and is considered only by the Neher-McGrathmethod.

Transient Load Profile

The load profile provides up to 20 time and current entry fields for specifying the loading pattern of the cable asa function of time.

In this example, the cable loading is changed from the steady-state (initial value) to 230 amperes at time zero,to 560 amps at time 3.5 hours, and finally to 400 amps after 7.3 hours. The steady-state or initial value caneither be 230 amps (value entered at the first time slot) or it can be set equal to the cable operating load. Youcan set the option for the initial/steady-state value from the Cable Derating Study Case Editor.

Time Unit

Select the time units for the load profile.

Optimization Options

These options are for ampacity and sizing calculations for the U/G raceway systems.

Fixed Current

If this box is checked, the cable current will remain unchanged for the ampacity calculations (UniformTemperature and Uniform Ampacity). Use this flag for cables that do not require ampacity optimization.

Fixed Size

# Time Current1 0.0 230

2 3.5 560

3 7.3 400

4 0.0 0.0 (all data from this

point are ignored

since time = 0.0 )



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If this box is checked, the cable size will remain fixed for the cable sizing calculations.

Cable Overview

Info Page

Impedance Page

Physical Page

Protection Page

Routing Page

Ampacit y Page

Sizing Page

Reliability Page

Remarks Page

Comment Page



-Ampacity Page - Cables

Calculation Methods and Standards

Dependent on the cable installation type, different methods can be used to calculate cable ampacity.

IEEE 399

This calculation method is according to the IEEE Std 399, IEEE Recommended Practice for Industrial andCommercial Power Systems Analysis. It covers installation types of underground duct and directly buried. Thecalculation is based on ampacity at a base condition and adjustment factors derived from detailed calculations usingthe Neher-McGrath method.

These factors establishe a maximum feasible load capacity, which results in no reduction of the cableexpectedlifetime. The overall derating factor is composed of several components as listed on the following page.

Fta = Derating factor for ambient temperature

Ftc = Derating factor for maximum allowable conductor temperature

Fth = Derating factor for underground soil thermal resistance

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Fg = Derating factor for cable grouping

Fc = Derating factor for A/G tray covers

Fm = Derating factor for A/G tray maintained spacing

Fce = Cumulative effect factor for A/G trays

Fm = Derating factor for A/G conduit (NEC and diversity factor)

Ffc = Derating factor for A/G fire coating

Ffs = Derating factor for A/G fire stop

Ffw = Derating factor for A/G fire wrap

ICEA P-54-440

The method based on ICEA P-54-440 applies to cables in above ground trays using calculated derating factorsbased on tray size, cable fill, and environment conditions. The actual values of tray depth, width, and % fill entrieswill be taken into account, which gives more accurate results and is based on the method described in the Stople

paper (Paper 70 TP 557-PWR)1. However, the Stople method may provide a smaller ampacity for large cables (for

example, 750 mm2

) compared to those from ICEA P-54-440.

In addition, if both the ambient temperature and conductor temperature differ from those shown in the ICEA

standard (400C ambient temperature and 90

0C conductor temperature), the resulting ampacity values may be

smaller because the standard used the product of both correction factors as the temperature correction. In ETAPcalculations, the ambient temperature and conductor temperature values are used directly in the calculation and,therefore, yield more accurate results.

In the used method, the following AC resistance equations for temperature corrections are employed:

R= R(234.5 + Tc) / (234.5 + Tb) Copper ConductorsR= R(228.1 + Tc) / (228.1 + Tb) Aluminum Conductors

Where:

R = Resistance at the base temperature Tb

R= Resistance at the operating temperature Tc

Tb = Conductor base temperature inO

C

Tc = Conductor temperature limit inO

C

NEC

This method calculates derating factors for cable trays according to NEC. It applies to cables in above ground trays,conduits, and air drop. NEC does not provide ampacity derating due to bottom cover or correction of the ampacitymultiplying factors due to the cumulative effects of combinations of tray covers and fireproofing. In general, cablesizes of 2/0 AWG and smaller are installed in cable trays in a randomly filled manner, with a maximum of two cableshigh.

Base ampacity of randomly filled trays are based on installations at a uniform depth up to the maximum of 30% fillfor 3 or 4-inch tray depths. The method applied here corresponds to a maximum fill condition and does not considerfill conditions exceeding the nominal depths.

BS 7671

This method is based on BS 7671 - 2001, Requirements for Electrical Installation. It applies to a number of types ofinstallation, including above ground and under ground configurations. This method can be used for cables atnominal voltages up to and including 1000V a.c. and 1500V d .c.

The displayed cable Base ambient temperature (Ta) is fixed at 30 Co

per BS 7671. The cable Base maximum



conductor temperature (Tc) is determined based on cable conductor type and insulation type corresponding toTables 4D1A and onwards of BS 7671.

Cable Base Ampacity is from Tables 4DA1 and onwards of BS 7671. Under certain conditions, the base ampacitymay not be available from these tables and the Base Aapacity field will show zero. In this case you may refer toETAP log pane for more information.

Cable Derated Ampacity is displayed in the Derated Ampacity field. The following derating factors are consideredfor cable derating calculation:

Ca Correction factor for ambient temperature. The factor is from Table 4C1 or Table 4C2 of BS 7671Appendix 4.

Cg Correction factor for grouping. The factor is from Tables 4B1, 4B2 or 4B3 of BS 7671 Appendix 4.

Ci Correction factor for conductors embedded in thermal insulation. Refer to Section 523-04 of BS 7671 fordetailed information.

Cf Correction factor for BS 3036 fuse. A factor of 0.725 is applied for cables protected by a fuse to BS 3036.Refer to Section 5 of BS 7671 Appendix 4 for detailed information. A BS 3036 Fuse is specified on theProtection page by selecting User-Defined Overload Protection device.

If a de-rating factor cannot be determined, the Derated Ampacity field on the Ampacity page will show zero. In thiscase you may refer to ETAP log pane for more information.

Sheath and Jacket LayerAccording to BS 7671, sheath layer is an important factor in ampacity calculation and the sheath layer can be eithermetallic or non-metallic. In the current version of ETAP, a sheath layer is only metallic: lead or aluminum. A Jackedin ETAP is treated as non-metallic sheath for BS 7671 based calculation. Therefore, for ampacity calculation basedon BS 7671, it is considered that the cable has a sheath layer if the cable has either a sheath layer or a jacket layer.It is required to enter a nonzero thickness value if a Sheath/Amor or Jacket Type is selected. Note that Paper typeJacket is not treated as a sheath for BS 7671 based calculation.

Flexible cable is not handled in this ETAP release.

Installation

The cable installation type can be specified based on the installation types or the standard used for calculation.

Standard

If the option of Standard is selected, the Standard list field contains all the calculation standards currently availablein ETAP, including IEEE 399, ICEA P-54-440, NEC, and BS 7671. When one of these standards is selected fromthe list, the Installation Type list will contain only the installation types applicable to the standard. The table belowgives all the installation types and applicable standards.

Type

If the option of Installation Type is selected, the Installation Type list field contains all the installation types currentlyavailable in ETAP. When one of these installation types is selected, the Standard list field will contain only thestandards applicable to the selected installation type. The table below gives all the installation types and applicablestandards.

App lic able Stand ards and Inst allatio n Types



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Sub-Type

When the BS 7671 standard appears in the Standard field, the installation sub-type and installation method will alsoshow up along with the installation type. You can select different installation sub-type from the list.

Method

This field displays the installation method for the selected sub-type per Table 4A1, BS 7671 : 2001, Requirements

for Electrical Installations.



Note: Magnetic/Non-magnetic Installation

Magnetically installed cables imply that there is a continuous raceway (conduit) around the cables with circulatingcurrent due to the magnetic field of the cables. This circulating current will cause the cable reactance (X1 and X0) toincrease by up to 15% for smaller size cables, and 5 to 10% for larger size cables. The following table shows when

to use cable libraries designated as Magnetically and Non-magnetically Installed cables:

Temperature/RHO

This section includes information about cable temperature and earth thermal resistivity if the installation type is U/GDuct or U/G Buried.

Base

Ta

This is the ambient temperature in degrees Celsius centimeter obtained from the library for the base ampacity. Theambient temperature is the temperature at a cable installation location when the cable installation is absent. Baseampacity for U/G cables are usually given at 20 degrees Celsius.

Tc

Conductor temperature in degrees Celsius obtained from the library for the base ampacity. This order is usuallygiven at 90 degrees Celsius.

Cable Library Header

MagneticallyInstalled

Non- MagneticallyInstalled

U/G Duct PVC Conduits X

U/G Duct Mag. Conduits X

U/G Buried X

A/G Tray No Cover X

A/G Tray Solid & Mag. Material X

A/G Conduit - PVC X

A/G Conduit Mag. Conduit

Air Drop X



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RHO

The thermal resistivity of the soil in degrees Celsius centimeters per Watt obtained from the library for the baseampacity. The fields for RHO will be hidden if the installation type is not U/G Duct or U/G Buried.

Operating

Ta

Ambient temperature for actual underground installations in degrees Celsius. The ambient temperature is thetemperature at the cable installation location when the installation is absent.

Tc

Maximum allowable conductor temperature for actual underground installations in degrees Celsius.

RHO

The thermal resistivity of the soil for actual underground installations in degrees Celsius centimeters per Watt.

Ampacity

Ampacity ratings are displayed for easy comparison of base, derated and, required (I x MF) ampacities. The methodused here is based on a concept of a derating factor that is applied against a base ampacity to calculate the deratedampacity.

Id = F x Ib

FLA / Operating

This field displays the required load current for the cable. For a branch cable, the required current will be the

Average operating current entered or updated by load flow calculations in the Loading page of the cable editor

For an equipment cable, the option of FLA/Operating will be enabled. If the FLA option is selected, the requiredcurrent is the full load ampere of the load. If the Operating option is selected, the required current will be theAverage operating current entered or updated by load flow calculations in the Loading page of the cable editor.

Base

The full rated current value in amperes for the chosen cable before any derating occurs. This is the ampacity statedor specified by the manufacturer or other authoritative sources, such as NEC or ICEA. Note that if the calculationstandard is ICEA P-54-440, this field is hidden, since the base ampacity is not required for the calculation by thestandard.

Derated

The modified base ampacity (maximum allowable current) in amperes for the chosen cable under the specifiedinstallation conditions.

Note: Overall Derating Factor (F)

Adjustment or correction factor which takes into account differences in the cableactual installation conditions fromthe base conditions. This factor establishes a maximum feasible load capacity, which results in no reduction of thecableexpected lifetime. The overall derating factor is composed of several components as listed on the followingpage.










Fm = Derating factor for A/G conduit (NEC & diversity factor)




Al lowable Ampaci ty (Alert)

This is the maximum allowable ampacity of the cable. It is used in the load flow output reports to indicate thepercent of cable overloading. This value is also used as a base for the cable flow constraint in the optimal powerflow studies.

ETAP provides options for selecting the maximum allowable current:

Tray

This section is enabled when the installation type is A/G Trays and the Standard is either ICEA P-54-440 or NEC.

Top Cover

Select Top Cover if there is a removable top cover on the cable tray.

Bottom Cover

Select bottom cover if there is a bottom cover on the cable tray, whether it is removable or solid, of more than 6feet.

Derated Select this option to make the derated ampacity the maximum allowablecurrent for this cable.

User-Defined Select this option to enter the maximum allowable current for this cable

UGSCalculated

Select this option to use the ampacity calculated by the UndergroundRaceways Systems module.



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Cumulative Effect

Cumulative effect applies correction factors for combinations of barriers, fire coatings, and covers on cable trays.The following table summarizes the factors ETAP uses:

Maintained Spacing

Check this box to indicate that cables are kept in the tray with maintained spacing.

Ampacity Adjustment

The Ampacity Adjustment section is enabled when the cable installation type is A/G conduit and the Standard isNEC. From this section, you can select options to consider grouping effect.

Without Grouping Effect

NEC standards do not allow for grouping effects (that is, the number of rows and columns) of cables. If the checkbox is not selected, grouping effects of number of rows and columns will be considered. Note that when this box ischecked, the Rows and Columns fields and the Fire Protection section will be hidden.

With 50% Load Diversity and Withou t Load DiversityThe level of load diversity used in calculating correction factors can be either 50% or none.

FireCoating

FireStop

Fire Wrap TopCover

BottomCover

PS Uses

X X Fire Wrap

X X Smaller

X X Smaller

X X X Top & Bottom

X X Wrap

X X Wrap

X X X Wrap



Layout

This section is enabled when the standard is BS 7671 and the installation type is one of the above ground types.

Horizontal

Select Horizontal layout with Touching or Spaced if applicable.

Vertical

Select Vertical layout with Touching or Spaced if applicable.

Trefoil

Select Trefoil layout.

Spaced

Select this option if the cables are placed with required spacing between them. Note that this field is hidden if it isnot applicable for the selected installation type.

Touching

Select this option if the cables are placed touching each other in the installation. Note that this field is hidden if it isnot applicable for the selected installation type.

Grouping

From this section, you specify installation information related to calculation of cable grouping factors. The fields inthis section are dependent on the installation type and standard selected.

Parameters in Grouping Section for IEEE 399 Standard, U/G Raceway

Grouped cables operate at higher temperatures than isolated cables. To derate the ampacity, the number of rowsand columns of the duct bank must be specified to determine a cable grouping adjustment factor.

The cable ampacity adjustment factors are based on 7.5 inches center-to-center spacing. For more details see theIEEE Brown Book.



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Parameters in Groupi ng Section for NEC Standard, A/G Conduit

Grouped cables operate at higher temperatures than isolated cables. To derate the cable ampacity, the number ofrows and columns of conduit installed next to each other, as well as the total number of conductors per location (thisconduit), can be specified to determine a cable grouping adjustment factor.

Parameters in Grouping Section for ICEA P-54-440 Standard, A/G Trays

The following items are displayed only when ICEA is selected.



Height

Height of cable tray specified in inches or centimeters

WidthWidth of cable tray specified in inches or centimeters

% Fill

The total amount of cable tray cross-sectional area used by cables placed in the tray, including gap between cables.

Where ni is the number of cables in the tray with diameter di and l is the number of different sizes of cables in thetray.

Depth

Depth of cable mess calculated in inches or centimeters using Height*%Fill/100. If the calculated depth is smallerthan the cable diameter, an * sign will be displayed on the right of Depth and above Derated, and the cablediameter will be treated as the depth for derating calculation.

Fire Protection fo r ICEA or NEC Standards, A/G Installation

The fire protection area provides optional libraries from which to choose various fire protection devices. Each of thethree libraries may be selected individually to best describe the fire protection associated with the cable tray. Thefire protection data is used to further derate cables based on the fire protection material specifications selected fromETAP library. The ampacity correction factors applied for fire protection is based on 10 CFR 50, Appendix R for FireWrap, Fire Stop, and Fire Coating.



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Fire Coating

The Fire Coating Library provides a selection of configurations. Each configuration has an ampacity correctionfactor (ACF) associated with it, which is applied against the base ampacity.

For maintained spacing trays, if the fire retardant coating results in a reduction of the spacing between adjacentcables or groups to less than the required values, the cable shall be considered to be non-maintained spacing. Onthe other hand, if remaining space in a randomly filled tray is used up by cable coating and no other cable can beinstalled in the tray; credit may be taken for a reduction in cable % fill below nominal value.

Fire retardant coating is not a standard procedure for A/G conduits.

Fire Stop

The Fire Stop Library provides a selection of configurations with ampacity correction factors for cables in tray routedthrough fire stops. Note: for A/G conduits, there may not be any reason to derate the cable for fire stops sincetypical fire stops are constructed with expanded foam depth of 4 inches or less. This is considered to be insufficient

to cause an increase in cable temperature.

Fire Wrap

The Fire Wrap Library provides a selection of configurations. Each fire barrier configuration has an ampacitycorrection factor (ACF) associated with it. This ACF must be applied whenever the raceway is wrapped for a lengthexceeding 6 feet and whenever the raceway has multiple, wrapped segments whose combined length exceeds 6feet and which are spaced less than 10 feet apart.

Fire Protection f or BS 7671 Standard, A/G Installation

This section is about thermal insulation. Refer to Section 523-04, BS 7671 for detailed information.

According to BS 7671, thermal insulation for fire protection may be considered for all installation types, exceptInstallation Methods 4 and 6. For Installation Method 4 or 6, cables are in conduits which are in thermally insulatedwall or above thermally insulated ceiling, and the effect of thermal insulation is already considered in the current-carrying capacity tables.



Thermal Insulation A pplied

Check this box if the cable has thermal insulation.

Insulation Length

Enter the length of able thermal insulation in mm.

Back to the top

U/G DuctUnderground duct banks encased in concrete.

Base

Ta

Ambient soil temperature in degrees Celsius centimeter per Watt obtained from the library for the base ampacity.Base ampacity for U/G cables are usually given at 20 degrees Celsius.

Tc


RHO

The thermal resistivity of the soil in degrees Celsius centimeters per Watt obtained from the library for the base

ampacity.

Operating

Ta

Ambient temperature (temperature of the surrounding soil) for actual underground installations in degrees Celsius.

Tc


RHO


Grouping


The cable ampacity adjustment factors are based on 7.5 inches center-to-center spacing. For more details see theIEEE Brown Book.

Back to the top

U/G BuriedDirectly buried underground ducts.



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Base

Ta

Ambient soil temperature in degrees Celsius centimeter per Watt obtained from the library for the base ampacity.Base ampacity for U/G cables are usually given at 20 degrees Celsius.

Tc


RHO

The thermal resistivity of the soil in degrees Celsius centimeters per Watt obtained from the library for the baseampacity.

Operating

Ta

Ambient temperature (that is, the temperature of the surrounding soil) in degrees Celsius for undergroundinstallations.

Tc

Maximum allowable conductor temperature is in degrees Celsius.

Grouping

Grouped cables operate at higher temperatures than isolated cables. To derate the cable ampacity, the number ofrows and columns of the cable locations must be specified to determine a cable grouping adjustment factor. Thecable ampacity adjustment factors are based on a 7.5-inch center-to-center spacing. For more details see the IEEE

Brown Book.

Back to the top

A/G TraysAbove ground cable trays. The free air base ampacity from the libraries are used for cables installed in trays.

Base

Ta

Ambient air temperature in degrees Celsius obtained from the library for the base ampacity. The value is usuallyspecified at 40 degrees Celsius

Tc

Maximum allowable conductor temperature in degrees Celsius obtained from the library. Conductor temperature forthe base ampacity is typically 90 degrees Celsius.

Operating

Ta

Ambient air (atmospheric) temperature (that is, the temperature of the air surrounding the area where the tray isinstalled) is in degrees Celsius.

Tc

Maximum allowable conductor temperature in degrees Celsius. Conductor temperature for the base ampacity istypically 90 degrees Celsius.



Tray

NEC

If chosen, NEC methods of calculating derating factors for cable trays will be used. NEC does not provide ampacityderating due to bottom cover or correction of the ampacity multiplying factors due to the cumulative effects ofcombinations of tray covers and fireproofing. In general, cable sizes of 2/0 AWG and smaller are installed in cabletrays in a randomly filled manner, with a maximum of two cables high.


ICEA

Select this option to choose an ICEA P-54-440 method of calculating derating factors for cable trays. The actual

values of tray depth, width, and % fill entries will be taken into account, which gives more accurate results and isbased on the method described in the Stople paper (Paper 70 TP 557-PWR)

1. However, the Stople method may

provide a smaller ampacity for large cables (for example, 750 mm2) compared to those from ICEA P-54-440.


standard (40 0C ambient temperature and 90 0C conductor temperature), the resulting ampacity values may besmaller because the standard used the product of both correction factors as the temperature correction. In ETAPcalculations, the ambient temperature and conductor temperature values are used directly in the calculation and,therefore, yield more accurate results.


R= R(234.5 + Tc) / (234.5 + Tb) Copper Conductors

R= R(228.1 + Tc) / (228.1 + Tb) Aluminum Conductors

Where:



Tb = Conductor base temperature inOC

Tc = Conductor temperature limit in OC

Top Cover


Bottom Cover

Select bottom cover if there is a bottom cover on the cable tray, whether it is removable or solid, of more than 6feet.

Maintained Spacing

If cable spacing is maintained within the tray, then the effects of top cover, bottom cover, and fire wrap are ignored.For 3-phase cables larger than 2/0 AWG in a single layer, the arrangement requires spacing of 1/4 of overalleffective diameter of the grouped circuit.

Cumulative EffectCumulative effect applies correction factors for combinations of barriers, fire coatings, and covers on cable trays.The following table summarizes the factors ETAP uses:



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Grouping

The following items are displayed only when ICEA is selected.

Height

Height of cable tray specified in inches or centimeters

Width

Width of cable tray specified in inches or centimeters

% Fill

The total amount of cable tray cross-sectional area used by cables placed in the tray, including gap between cables.

Where ni is the number of cables in the tray with diameter di and l is the number of different sizes of cables in thetray.

DepthDepth of cable mess calculated in inches or centimeters using Height*%Fill/100. If the calculated depth is smallerthan the cable diameter, an * sign will show up on the right of Depth andabove Derated, and the cable diameterwill be treated as the depth for derating calculation.

FireCoating

FireStop

Fire Wrap TopCover

BottomCover

PS Uses .

X X Fire Wrap

X X Smaller

X X Smaller

X X X Top & Bottom

X X Wrap

X X Wrap

X X X Wrap



Fire Protection

The fire protection area provides optional libraries from which to choose various fire protection devices. Each of thethree libraries may be selected individually to best describe the fire protection associated with the cable tray. Thefire protection data is used to further derate cables based on the fire protection material specifications selected fromETAP library. The ampacity correction factors applied for fire protection is based on 10 CFR 50, Appendix R for FireWrap, Fire Stop, and Fire Coating.

Fire Coating

The Fire Coating Library provides a selection of configurations. Each configuration has an ampacity correctionfactor (ACF) associated with it, which is applied against the base ampacity. For maintained spacing trays, if the fireretardant coating results in a reduction of the spacing between adjacent cables or groups to less than the requiredvalues, the cable shall be considered to be non-maintained spacing. On the other hand, if remaining space in arandomly filled tray is used up by cable coating and no other cable can be installed in the tray; credit may be takenfor reduction in cable % fill below nominal value.

Fire Stop

The Fire Stop Library provides a selection of configurations with ampacity correction factors for cables in tray routedthrough fire stops.

Fire Wrap

The Fire Wrap Library provides a selection of configurations. Each fire barrier configuration has an ampacitycorrection factor (ACF) associated with it. This ACF must be applied whenever the raceway is wrapped for a lengthexceeding 6 feet and whenever the raceway has multiple, wrapped segments whose combined length exceeds 6feet and which are spaced less than 10 feet apart.

Back to the top

A/G ConduitAbove ground cable conduit

Base

Ta

This is the ambient air (atmospheric) temperature is in degrees Celsius obtained from the library.

Tc

This is the maximum allowable conductor temperature is in degrees Celsius obtained from the library.

Operating

Ta

This is the ambient air (atmospheric) temperature is in degrees Celsius. It is the temperature of the air surroundingthe area where the tray is to be installed. The value is usually specified at 40 degrees Celsius.



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Tc

This is the maximum allowable conductor temperature is in degrees Celsius. The value is usually specified at 90degrees Celsius.

Ampacity Adjustment

NEC w/o Grouping Effect

NEC standards do not allow for grouping effects (that is, the number of rows and columns) of cables. If the checkbox is not selected, grouping effects of number of rows and columns will be considered.

NEC w/ 50% Load Diversit y & NEC w/o Load Diversit y

The level of load diversity used in calculating correction factors can be either 50% or none.

Grouping

Grouped cables operate at higher temperatures than isolated cables. To derate the cable ampacity, the number ofrows and columns of conduit installed next to each other, as well as the total number of conductors per location (thisconduit), can be specified to determine a cable grouping adjustment factor.

# of conductors per l ocation = (# of conductors per cable) x (# of cables per location)

Fire Protection

Fire protection provides optional libraries to choose various fire protection method. Each of the three libraries maybe selected individually to best describe the fire protection associated with the conduit. The fire protection data isused to further derate the cable ampacities based on the fire protection material specifications selected from ETAPlibrary. The ampacity correction factors applied for fire protection is based on 10 CFR 50, Appendix R for Fire Wrap,Fire Stop, and Fire Coating.

Fire Coating

The Fire Coating Library provides a selection of configurations from which to choose. Each configuration has anampacity correction factor (ACF) associated with it, which is applied against the base ampacity. Fire retardantcoating is not a standard procedure for A/G conduits.

Number of Conduc tors Ampac ity Correc tion Fac tor

50 % Load Diversity

4 through 6 80 %

7 through 9 70 %

10 through 24 70 %

25 through 42 60 %

43 and above 50 %

Number of Conductors Ampacit y Cor rect ion Facto r

No Load Diversity

4 through 6 80 %

7 through 9 70 %

10 through 20 50 %

21 through 30 45 %

31 through 40 40 %

41 through 60 35 %



Fire Stop

The Fire Stop Library provides a selection of configurations with ampacity correction factors for conduits routedthrough fire stops. Note: there may not be any reason to derate the cable for fire stops since typical fire stops areconstructed with expanded foam depth of 4 inches or less. This is considered to be insufficient to cause an increasein cable temperature.

Fire Wrap

The Fire Wrap Library provides a selection of configurations. Each fire barrier configuration has an ampacitycorrection factor (ACF) associated with it which must be applied whenever the raceway is wrapped for a lengthexceeding 6 feet and whenever the raceway has multiple, wrapped segments whose combined length exceeds 6feet and which are spaced less than 10 feet apart.

Air Drop

Air drop consists of cables suspended without the use of trays or conduits. No cable grouping for air drop cables areconsidered.

Base

Ta

This is the ambient air (atmospheric) temperature from the library in degrees Celsius.

Tc

This is the maximum allowable conductor temperature is in degrees Celsius obtained from the library.

Operating

TaThis is the ambient air (atmospheric) temperature. The temperature of the air surrounding the area where the tray isto be installed is in degrees Celsius. Ambient air temperature for the base ampacity is 40 degrees Celsius. Forcables in direct sunlight, the air temperature may be increased by a typical value of 15 degrees Celsius.

Operating Tc

This is the maximum allowable conductor temperature is in degrees Celsius. Conductor temperature for the baseampacity is 90 degrees Celsius.

Fire Protection

Fire Protection provides optional libraries to choose various fire protection devices. Each of the three libraries maybe selected individually to best describe the fire protection associated with the airdrop cables. The fire protectiondata is used to further derate the cable based on the fire protection specifications selected from ETAP library is

based on 10 CFR 50, Appendix R for Fire Wrap, Fire Stop, and Fire Coating.

Fire Coating

The Fire Coating Library provides a selection of configurations. Each configuration has an ampacity correctionfactor (ACF) associated with it, which is applied against the base ampacity.

Fire Stop

The Fire Stop Library provides a selection of configurations with ampacity correction factors for cables routedthrough fire stops.

Fire Wrap

The Fire Wrap Library provides a selection of configurations. Each fire barrier configuration has an ampacitycorrection factor (ACF) associated with it. The ACF must be applied whenever the cable is wrapped for a length

exceeding 6 feet and whenever the raceway has multiple, wrapped segments whose combined length exceeds 6feet and which are spaced less than 10 feet apart.



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References:

1. J. Stolpe, "Ampacities for Cables in Ramcomly Filled Trays," IEEE Summer Power Meeting and EHVConference, LA, Calif., July 12-17, 1970.

Cable Overview

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Sizing Page

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-Ampacity Page - Cables

Calculation Methods and Standards

Dependent on the cable installation type, different methods can be used to calculate cable ampacity.

IEEE 399

This calculation method is according to the IEEE Std 399, IEEE Recommended Practice for Industrial andCommercial Power Systems Analysis. It covers installation types of underground duct and directly buried. Thecalculation is based on ampacity at a base condition and adjustment factors derived from detailed calculations usingthe Neher-McGrath method.

These factors establishe a maximum feasible load capacity, which results in no reduction of the cableexpectedlifetime. The overall derating factor is composed of several components as listed on the following page.






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Fm = Derating factor for A/G conduit (NEC and diversity factor)




ICEA P-54-440

The method based on ICEA P-54-440 applies to cables in above ground trays using calculated derating factorsbased on tray size, cable fill, and environment conditions. The actual values of tray depth, width, and % fill entrieswill be taken into account, which gives more accurate results and is based on the method described in the Stople

paper (Paper 70 TP 557-PWR)1. However, the Stople method may provide a smaller ampacity for large cables (for

example, 750 mm2

) compared to those from ICEA P-54-440.


standard (400C ambient temperature and 90

0C conductor temperature), the resulting ampacity values may be

smaller because the standard used the product of both correction factors as the temperature correction. In ETAPcalculations, the ambient temperature and conductor temperature values are used directly in the calculation and,therefore, yield more accurate results.


R= R(234.5 + Tc) / (234.5 + Tb) Copper ConductorsR= R(228.1 + Tc) / (228.1 + Tb) Aluminum Conductors

Where:



Tb = Conductor base temperature inO

C

Tc = Conductor temperature limit inO

C

NEC

This method calculates derating factors for cable trays according to NEC. It applies to cables in above ground trays,conduits, and air drop. NEC does not provide ampacity derating due to bottom cover or correction of the ampacitymultiplying factors due to the cumulative effects of combinations of tray covers and fireproofing. In general, cablesizes of 2/0 AWG and smaller are installed in cable trays in a randomly filled manner, with a maximum of two cableshigh.


BS 7671

This method is based on BS 7671 - 2001, Requirements for Electrical Installation. It applies to a number of types ofinstallation, including above ground and under ground configurations. This method can be used for cables at

nominal voltages up to and including 1000V a.c. and 1500V d .c.

The displayed cable Base ambient temperature (Ta) is fixed at 30 Co

per BS 7671. The cable Base maximum



conductor temperature (Tc) is determined based on cable conductor type and insulation type corresponding toTables 4D1A and onwards of BS 7671.

Cable Base Ampacity is from Tables 4DA1 and onwards of BS 7671. Under certain conditions, the base ampacitymay not be available from these tables and the Base Aapacity field will show zero. In this case you may refer toETAP log pane for more information.

Cable Derated Ampacity is displayed in the Derated Ampacity field. The following derating factors are consideredfor cable derating calculation:

Ca Correction factor for ambient temperature. The factor is from Table 4C1 or Table 4C2 of BS 7671Appendix 4.

Cg Correction factor for grouping. The factor is from Tables 4B1, 4B2 or 4B3 of BS 7671 Appendix 4.

Ci Correction factor for conductors embedded in thermal insulation. Refer to Section 523-04 of BS 7671 fordetailed information.

Cf Correction factor for BS 3036 fuse. A factor of 0.725 is applied for cables protected by a fuse to BS 3036.Refer to Section 5 of BS 7671 Appendix 4 for detailed information. A BS 3036 Fuse is specified on theProtection page by selecting User-Defined Overload Protection device.

If a de-rating factor cannot be determined, the Derated Ampacity field on the Ampacity page will show zero. In thiscase you may refer to ETAP log pane for more information.

Sheath and Jacket Layer

According to BS 7671, sheath layer is an important factor in ampacity calculation and the sheath layer can be eithermetallic or non-metallic. In the current version of ETAP, a sheath layer is only metallic: lead or aluminum. A Jackedin ETAP is treated as non-metallic sheath for BS 7671 based calculation. Therefore, for ampacity calculation basedon BS 7671, it is considered that the cable has a sheath layer if the cable has either a sheath layer or a jacket layer.It is required to enter a nonzero thickness value if a Sheath/Amor or Jacket Type is selected. Note that Paper typeJacket is not treated as a sheath for BS 7671 based calculation.

Flexible cable is not handled in this ETAP release.

Installation

The cable installation type can be specified based on the installation types or the standard used for calculation.

Standard

If the option of Standard is selected, the Standard list field contains all the calculation standards currently availablein ETAP, including IEEE 399, ICEA P-54-440, NEC, and BS 7671. When one of these standards is selected fromthe list, the Installation Type list will contain only the installation types applicable to the standard. The table belowgives all the installation types and applicable standards.

Type

If the option of Installation Type is selected, the Installation Type list field contains all the installation types currentlyavailable in ETAP. When one of these installation types is selected, the Standard list field will contain only thestandards applicable to the selected installation type. The table below gives all the installation types and applicablestandards.

App lic able Stand ards and Inst allatio n Types



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Sub-Type

When the BS 7671 standard appears in the Standard field, the installation sub-type and installation method will alsoshow up along with the installation type. You can select different installation sub-type from the list.

Method

This field displays the installation method for the selected sub-type per Table 4A1, BS 7671 : 2001, Requirementsfor Electrical Installations.



Note: Magnetic/Non-magnetic Installation

Magnetically installed cables imply that there is a continuous raceway (conduit) around the cables with circulatingcurrent due to the magnetic field of the cables. This circulating current will cause the cable reactance (X1 and X0) toincrease by up to 15% for smaller size cables, and 5 to 10% for larger size cables. The following table shows when

to use cable libraries designated as Magnetically and Non-magnetically Installed cables:

Temperature/RHO

This section includes information about cable temperature and earth thermal resistivity if the installation type is U/GDuct or U/G Buried.

Base

Ta

This is the ambient temperature in degrees Celsius centimeter obtained from the library for the base ampacity. Theambient temperature is the temperature at a cable installation location when the cable installation is absent. Baseampacity for U/G cables are usually given at 20 degrees Celsius.

Tc


Cable Library Header

MagneticallyInstalled

Non- MagneticallyInstalled

U/G Duct PVC Conduits X

U/G Duct Mag. Conduits X

U/G Buried X

A/G Tray No Cover X

A/G Tray Solid & Mag. Material X

A/G Conduit - PVC X

A/G Conduit Mag. Conduit

Air Drop X



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RHO

The thermal resistivity of the soil in degrees Celsius centimeters per Watt obtained from the library for the baseampacity. The fields for RHO will be hidden if the installation type is not U/G Duct or U/G Buried.

Operating

Ta

Ambient temperature for actual underground installations in degrees Celsius. The ambient temperature is thetemperature at the cable installation location when the installation is absent.

Tc


RHO


Ampacity

Ampacity ratings are displayed for easy comparison of base, derated and, required (I x MF) ampacities. The methodused here is based on a concept of a derating factor that is applied against a base ampacity to calculate the deratedampacity.

Id = F x Ib

FLA / Operating

This field displays the required load current for the cable. For a branch cable, the required current will be the

Average operating current entered or updated by load flow calculations in the Loading page of the cable editor

For an equipment cable, the option of FLA/Operating will be enabled. If the FLA option is selected, the requiredcurrent is the full load ampere of the load. If the Operating option is selected, the required current will be theAverage operating current entered or updated by load flow calculations in the Loading page of the cable editor.

Base

The full rated current value in amperes for the chosen cable before any derating occurs. This is the ampacity statedor specified by the manufacturer or other authoritative sources, such as NEC or ICEA. Note that if the calculationstandard is ICEA P-54-440, this field is hidden, since the base ampacity is not required for the calculation by thestandard.

Derated

The modified base ampacity (maximum allowable current) in amperes for the chosen cable under the specifiedinstallation conditions.

Note: Overall Derating Factor (F)

Adjustment or correction factor which takes into account differences in the cableactual installation conditions fromthe base conditions. This factor establishes a maximum feasible load capacity, which results in no reduction of thecableexpected lifetime. The overall derating factor is composed of several components as listed on the followingpage.










Fm = Derating factor for A/G conduit (NEC & diversity factor)




Al lowable Ampaci ty (Alert)

This is the maximum allowable ampacity of the cable. It is used in the load flow output reports to indicate thepercent of cable overloading. This value is also used as a base for the cable flow constraint in the optimal powerflow studies.

ETAP provides options for selecting the maximum allowable current:

Tray

This section is enabled when the installation type is A/G Trays and the Standard is either ICEA P-54-440 or NEC.

Top Cover


Bottom CoverSelect bottom cover if there is a bottom cover on the cable tray, whether it is removable or solid, of more than 6feet.

Derated Select this option to make the derated ampacity the maximum allowablecurrent for this cable.

User-Defined Select this option to enter the maximum allowable current for this cable

UGSCalculated

Select this option to use the ampacity calculated by the UndergroundRaceways Systems module.



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Cumulative Effect

Cumulative effect applies correction factors for combinations of barriers, fire coatings, and covers on cable trays.The following table summarizes the factors ETAP uses:

Maintained Spacing

Check this box to indicate that cables are kept in the tray with maintained spacing.

Ampacity Adjustment

The Ampacity Adjustment section is enabled when the cable installation type is A/G conduit and the Standard isNEC. From this section, you can select options to consider grouping effect.

Without Grouping Effect

NEC standards do not allow for grouping effects (that is, the number of rows and columns) of cables. If the checkbox is not selected, grouping effects of number of rows and columns will be considered. Note that when this box ischecked, the Rows and Columns fields and the Fire Protection section will be hidden.

With 50% Load Diversity and Withou t Load Diversity

The level of load diversity used in calculating correction factors can be either 50% or none.

FireCoating

FireStop

Fire Wrap TopCover

BottomCover

PS Uses

X X Fire Wrap

X X Smaller

X X Smaller

X X X Top & Bottom

X X Wrap

X X Wrap

X X X Wrap



Layout

This section is enabled when the standard is BS 7671 and the installation type is one of the above ground types.

Horizontal

Select Horizontal layout with Touching or Spaced if applicable.

Vertical

Select Vertical layout with Touching or Spaced if applicable.

Trefoil

Select Trefoil layout.

Spaced

Select this option if the cables are placed with required spacing between them. Note that this field is hidden if it isnot applicable for the selected installation type.

Touching

Select this option if the cables are placed touching each other in the installation. Note that this field is hidden if it isnot applicable for the selected installation type.

Grouping

From this section, you specify installation information related to calculation of cable grouping factors. The fields inthis section are dependent on the installation type and standard selected.

Parameters in Grouping Section for IEEE 399 Standard, U/G Raceway


The cable ampacity adjustment factors are based on 7.5 inches center-to-center spacing. For more details see theIEEE

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